Conventionally, a refrigerant radiator for a vapor compression refrigerant cycle is known, in which high-temperature and high-pressure refrigerant discharged from a compressor radiates heat through heat exchange with air. For example, Patent Document 1 (JP 2004-125346 A) discloses regarding a refrigerant radiator for a vapor compression refrigerant cycle, which is used for a vehicle air conditioner. The refrigerant radiator functions as a portion heating air blown into an internal space of a vehicle compartment, which is a space to be air-conditioned. The air to be blown into the vehicle compartment is heated by performing heat exchange with refrigerant discharged from a compressor, in the refrigerant radiator.
The refrigerant cycle described in Patent Document 1 is a supercritical refrigerant cycle, in which carbon dioxide is adopted as refrigerant and a refrigerant pressure in a high-pressure-side part of the cycle between an outlet of the compressor and an inlet of a decompression device is higher than a supercritical pressure of refrigerant. Therefore, in the refrigerant radiator described in Patent Document 1, refrigerant radiates heat in a supercritical state without phase transition.
However, if the refrigerant radiator in Patent Document 1 is used for a subcritical refrigerant cycle, in which the refrigerant pressure in the high-pressure-side part of the cycle is lower than the supercritical pressure of refrigerant, it may be difficult to sufficiently limit inhomogenization of temperature distribution of air blown into the vehicle compartment. The reason is that refrigerant changes from overheated gas-phase refrigerant into gas-liquid two-phase refrigerant, and furthermore, changes into supercooled liquid-phase refrigerant in the subcritical refrigerant cycle. In the subcritical refrigerant cycle, when refrigerant in the refrigerant cycle is in a gas or liquid phase, the refrigerant radiates heat with decreasing its temperature, i.e., both the temperature and enthalpy of the refrigerant reduce. However, when refrigerant is in a gas-liquid phase, only the enthalpy of refrigerant reduces while the refrigerant radiates heat without decreasing its temperature.
In the refrigerant radiator in Patent Document 1, a heat exchange area, where refrigerant is in the gas-liquid phase, and another heat exchange area, where refrigerant is in the gas or liquid phase, may be overlapped in a flow direction of air flowing into the refrigerant radiator. Therefore, temperature difference may be caused in air blown from the refrigerant radiator.
Furthermore, if air flowing out of the refrigerant radiator has the inhomogeneous temperature distribution, there may be a heat exchange area in the refrigerant radiator, where temperature difference between air flowing into the refrigerant radiator and refrigerant cannot be ensured enough. Hence, heat radiation ability of the whole refrigerant radiator may reduce. Such the reduction of heat radiation ability may cause increase of enthalpy of refrigerant flowing into an evaporator of the refrigerant cycle, and thereby it may reduce coefficient of performance (COP) of the refrigerant cycle.